Mesoporous MCM-41 was functionalized using magnesium nitrate hexahydrate (denoted as MM). The adsorption behavior of Cd²⁺ on functionalized MCM-41 was investigated systematically. The adsorption isotherms of MM for Cd(II) could be described by the Langmuir isotherm model. The adsorption rates were very high and agreed well with pseudo second-order kinetics. The modified MCM-41 adsorbent displayed excellent Cd²⁺ adsorption efficiency (210.96 mg g⁻¹) and the residual concentration of Cd²⁺ achieved was in line with drinking water quality standards. The regeneration capacity maintained 99% performance when the initial solution concentration was 5 mg L⁻¹ (5000 ppb) at the eighth cycle, meeting the safe regulatory discharge standard for the first time. Furthermore, regeneration by an ultrasonic cleaning method to remove residual surface Cd²⁺ can reduce both the cost of traditional desorption agents and damage to the structure of the adsorbent. Therefore, the adsorbent MM has potential as a promising application in the field of water pollution control.